ignore SIGPIPE
do not forget to return on error
[http2] do not start a pending request while trying to close the connection on error
[refactor] move timeout impl to socket_loop.c / run the pending callbacks enqueued by timeout callbacks
[linux] include signal.h
fix degrade in 44e90b95
handle zero-second timeouts specially, since all of them along with pending callbacks should be called prior to calling poll)